At the time that syntax highlighting DOM was introduced, the offsets of
selection ranges had been broken. In change [1] Kasper fixed this for
GR-DIFF-HIGHLIGHT with selection normalization functions. However,
selections for copying code as implemented in GR-DIFF-SELECTION were
still un-normalized.
With this change, the normalization functionality introduced in [1] is
moved to a JS library so that it can be used by both components. Tests
are updated.
[1] I26c61ca706575ea5df6e3b7b18a27225834396e8
Change-Id: I35ab0f71a46b3fc1d7356a314a0cae856f2ef28e
